The present disclosure relates to a photonic integrated circuit comprising a ring resonator and a method for interrogating a ring resonator in a photonic integrated circuit.
A photonic integrated circuit (IC) also known as an integrated optical circuit is a device that integrates photonic functions. Light traversing the circuit can be guided and/or processed by the circuit. One example of a photonic integrated circuit comprises a ring resonator arranged in proximity between a first waveguide and a second waveguide. Light in the waveguides may be coupled to the ring, e.g. by an evanescent field. In this way light may travel via the ring from the first waveguide to the second waveguide. The ring may have one or more resonant wavelengths that are selectively or predominantly passed between the waveguides. A resonant wavelength of the ring can depend on a physical parameter influencing the ring. Accordingly, the ring can exhibit a spectral signature that can be used to quantify said physical parameter, e.g. temperature, pressure, chemical data, etc.
The circuit can be interrogated (read out) by an analyser. For example, the analyser can couple light into the first waveguide of the circuit and detect output light from the second waveguide of the circuit to measure the spectral signature of the optical sensing element and quantify the physical parameter. The analyser can be a separate instrument for interrogating the photonic circuit, e.g. integrated on a chip. In this way different circuits can be interrogated by a single instrument. To provide a flexible connection between the analyser and circuit, light can be free-space coupled into the circuit via an optical port, e.g. a vertical grating coupler. For example, the analyser comprises an objective lens, or an optical fibre that is brought in close proximity to the optical port.
Typically, separate ports are used to couple light in and out of the circuit. In order to reduce complexity, it can be advantageous to have as few optical connections as possible. This can make alignment procedures between the circuit and analyser easier. For instance if a single port can be employed to couple light in and out of the circuit, the coupling can be more tolerant to rotation of the circuit e.g. with respect to the fibre around the optical axis. This can make implementation in a hand-held device, e.g. for point-of-care diagnostics more feasible. It has been tried to interrogate a ring resonator via a single conventional vertical grating coupler. However, the response was found to be of poor quality.
Accordingly, there is a desire to improve response quality of the photonic integrated circuit comprising a ring resonator interrogated via a single optical port.